Automatic tracking systems are widely used for various military and nonmilitary purposes. Among the military purposes are the determination of the locations of airborne, undersea, and seaborne vehicles in a region to be controlled, and the automatic control of weapons directed toward such targets. Air traffic and harbor traffic control are among the civilian or peacetime uses of automatic tracking systems.
FIG. 1 is a simplified block diagram of a prior-art target tracking system 10. In FIG. 1, a sensor or sensor array designated 12 observes a region 14 in which one or more targets T are maneuvering. An arrow 16 illustrates the instantaneous velocity of target T. Sensor 12 may be a radar, sonar, or lidar system, a staring optical array, an acoustic system, or any sensor which is capable of sensing information relating to the position and velocity state of the target T. Sensor 12 may include a receiver in some cases.
State information from sensor 12 of FIG. 1 is coupled by a path 18 to a tracker designated generally as 20. Path 18 may be an electrical, optical or acoustic path, and may carry analog, digital, or other signals. Tracker 20 includes a corrector or estimator 24 which receives difference or residual information from a subtractor or difference signal generator (also known as an error detector) 26, and which processes the signal to produce a better estimate of the state of the target(s). The predicted state of the target is fed back to the inverting (−) input port of subtraction circuit 26 by way of a predictor (into the future) or propagator illustrated as a block 28. The predicted state of the target applied to the inverting input port of the subtracting circuit is compared with the actual sensed state applied to the noninverting (+) input port to produce the residual which is applied to the corrector 24. The corrected state produced by corrector 24 is made available for use, as for example by applying the state information to a display unit 30. The name generally given to a tracker such as 20 of FIG. 1 is “Kalman filter”.
Those skilled in the art know that predictors such as 28 of FIG. 1, and the Kalman filter generally, make certain assumptions about the characteristics of the target. For example, a predictor may operate on the assumption that the target's current velocity is the velocity which it will have in the future. If such a predictor is used in a situation in which the target accelerates, the prediction of the future state may be in error. Put another way, the target may maneuver by varying speed, direction, and the like, and such maneuvers may adversely affect the predicted state.
A maneuver detector illustrated as a block 32 is coupled to receive the residual information from error detector 26 of FIG. 1. The purpose of maneuver detector 32 is to declare the presence of maneuvering in the presence of deviation from constant velocity. The output of the maneuver detector 32 is coupled to a utilization apparatus. In the particular case illustrated in FIG. 1, the declaration from the maneuver detector 32 is applied by way of a threshold 34 to the display 30 (as an alternative viewpoint, threshold 34 is part of maneuver detector 32). If the target is not accelerating, the residual is expected to be zero-mean white noise. In the presence of acceleration, the residuals will develop a bias (an average value greater or less than zero) which is indicative of the amount of acceleration. Various types of maneuver detectors have been used in the prior art. Among the prior-art maneuver detectors are those that average the residuals to determine the presence or absence of a bias. Another prior-art scheme uses inverse exponential weighting of residuals, also known as “fading memory.” The maneuver detector 32 of FIG. 1, which is coupled to a threshold illustrated as a block 34, which determines if the bias exceeds a given level, and thus exceeding the threshold is indicative of a maneuver by the target. The output of the maneuver detector 32 and threshold 34, if any, is coupled to a utilization apparatus, which may be, for example, display 30, to advise the operator that the indicated track may not be accurate.
FIG. 2 illustrates another prior-art system 200 similar to that of FIG. 1, in which the maneuver declaration information generated by maneuver detector 32 and tested by threshold 34 is applied not only to display 30, but also by way of a path 36 to corrector 24, so that the tracking parameters of the corrector may be adjusted, generally by loosening the bounds, in the presence of a maneuver.
Target tracking with improved or alternative maneuver detection is desired.